(1) Field of the Invention
The present invention relates to a damper device, and to an aircraft including at least one lead/lag damper device of this type.
The invention relates to the general technical field of damping movements in a mechanical system, and more particularly to the field of equipment including damper systems for use in aviation.
The invention is applicable in any damper system, and in particular in lead/lag dampers used on a lift rotor of a rotorcraft, and in particular of a helicopter. The invention is thus situated in the narrow technical field of lead/lag dampers.
(2) Description of Related Art
On a helicopter rotor, a damper device may connect each blade to the hub of the rotor or may connect together two consecutive blades. Such a damper device is known in particular as a “lead/lag” damper.
The combination of the flapping movement of the blades and of the rotary movement of the blades about the axis of rotation of the rotor leads to a Coriolis force appearing, i.e. a periodic force that causes the blades to oscillate in their plane of rotation. Consequently, a damper device connected to a blade of a rotorcraft rotor serves firstly to damp the oscillations of the blade performing lead/lag movement. The stiffness of the damper device thus limits the amplitude of the lead/lag movement of the blade in flight.
Such a damper device can serve secondly to at least limit the risk of the appearance of resonance phenomena known as “ground” resonance and as “air” resonance.
Consequently, a damper device presents stiffness that is designed so that the resonant frequency of the blades of a rotor during lead/lag movement is appropriate to satisfy dimensional requirements for good operation of the rotor, e.g. with respect to the ground resonance phenomenon. Furthermore, a damper device is also designed to damp the lead/lag movements of the blades in order to limit any risk of entering into ground resonance when the resonant frequency about stationary axes of the rotor blade during lead/lag movement is equal to an excitation frequency of the fuselage of the aircraft standing on its landing gear.
Likewise, the damping provided by a damper device seeks to combat the phenomenon of air resonance.
In order to generate an appropriate damping relationships, it is known to use particular damper devices. In general, these damper devices are based on a characteristic relationship for a force as a function of the dynamic movement of the damper device. The relationship presents three distinct damping ranges depending on the dynamic movement to which the lead/lag damper is subjected.
Such a relationship is referred to as a “triple slope” type relationship. Specifically, the relationship presents a first segment corresponding to the operation required for combating the ground resonance phenomenon, a second segment corresponding to the operation required in flight, and a third segment for combating the air resonance phenomenon.
In this context, a known damper device presents resilient members only, such as springs.
Another known damper device presents a hydraulic system only.
Another damper device is a “mixed” damper. A mixed damper device has both a hydraulic system and a resilient member.
Document FR 2 950 027 describes a damper device having a plurality of blocks of elastomer.
Document CN 102 501 970 also describes a system having a plurality of blocks of elastomer.
A known mixed damper device is provided with a hydraulic system and with a resilient member arranged in parallel between two connection members.
A first connection member is secured to a strength member referred to as an “intermediate” strength member. The intermediate strength member includes a ring carrying a piston.
A second connection member is secured to a strength member referred to as the “central” strength member and to a strength member referred to as the “external” strength member, which strength members are arranged radially on either side of the intermediate strength member. An annular block of elastomer of the resilient member is secured to the intermediate strength member and to the external strength member. In contrast, hydraulic chambers of a hydraulic system are defined by the intermediate strength member and the central strength member.
A movement of the first connection member relative to the second connection member then stresses both the resilient member and the hydraulic system.
Nevertheless, it is found that such a mixed damper device can be difficult to maintain. For example, it may be necessary to disassemble the damper device completely in order to replace the resilient member, because of the physical link that exists between the resilient member and the hydraulic system. A failure of the resilient member thus leads to onerous maintenance actions. Unfortunately, resilient members, in particular members made of elastomer, can present a lifetime that is limited.
Document FR 2 592 696 describes a damper device of that type.
Document US 2013/0164131 also describes a damper device of that type. A first elastomer ring extends radially between an intermediate strength member and a central strength member, and a second elastomer ring extends radially between an intermediate strength member and an external strength member.
Document EP 2 678 222 describes a damper device having a first connection member secured to a hydraulic system. A second connection member is secured to a strength member, a resilient member being interposed between the strength member and the hydraulic system. The connection member and the hydraulic system operate in series as a result of the first connection member moving relative to the second connection member, i.e. one after the other.
Documents WO 2012/148389, WO 2013/152300, US 2012/0141276, and WO 2010/129322 are also known.
Document US 2012/0141276 describes a damper device having a resilient member defining a hydraulic chamber in part.